m257876

Hi everybody_

I've got a 1987 with a Nash 4+3, and 59,xxx miles on it. My dad got it for me last fall, and he bought it from a guy who had left it sitting in a barn (covered) for 8 years. So it sat a while.

I've been driving it this spring, usually just on the weekends. I've changed all the fluids out and replaced the clutch hydraulics since last fall. I reckon I've put maybe 200 miles on it.

There has been a small oil leak for the past month. I notice oil on the garage floor, and on the driver's side exhaust downstream of the manifold but before it gets back about to the clutch slave cylinder, there's an expansion that looks like a small muffler (not sure what that part is called). When the car gets warmed up and hot, a little oil has been dripping on that section of the exhaust, and it smokes.

Today, everything changed. I was coming home from church, and I noticed when I walked up to the car that there was an oil trail from the spot where I stopped & put it in R to back into my parking spot, all the way back to the car. Not a few drops - a solid trail. I live 5 minutes from church, so I peeked under the car, saw a small pool of oil, checked the dipstick (halfway between Low and Full), and drove home at low RPM.

I trailed oil all the way down my street, all the way into my garage, shut the engine down, and noticed lots of "burning oil smoke" coming out from under the car. It was that same section of the exhaust, but now it was clearly getting more oil on it than before. A pool of oil (12-18" diameter) quickly formed on the garage floor in the vicinity right under the oil filter. I pulled the dipstick and it was dry.

I put it up on stands and got under there to see if I could tell where the oil was coming from, but it was hard to tell for sure.

Question: what are the potential problems this might be? I haven't had the car long enough to learn the typical issues and most likely causes of an oil leak like this one. I'm just wondering what the typical suspects might be.

Thanks everybody,

Mark

Benny42

The oil filter gasket and the oil cooler that is sandwiched between the block & the filter (if your car has one & it probably does) are the primary suspects. The oil pressure senders and switches are also common leak points. They are in that area of the engine bay. The oil is dripping onto your one of your catalytic converters (you have 3).
Welcome to the forum. Post a pic if you can.

Tod Stiles

I think that the way you describe it you're going to want to look at the oil pressure sender and switch located right next to the distributor, just above the area you describe.

m257876

Thanks for the replies. I've got a friend with a garage/lift and 2 Corvettes ('88 and '03), and he lives about 4 miles from my house.

I think when he's got a free day, I'm going to fill up the crankcase, drive down to his house, and stick it straight up on the lift to look for the leak while the engine is still warm and hopefully there's still some oil coming out. We might even refill it, crank it and let it idle while it's up on the lift, in case that helps identify the location.

I'll try to remember to take some pics.

Btw - his first impression when I called him and told him what happened was that the rear main seal might have failed.

Thanks again everybody,

M

ctmccloskey

The above answers are the first places to check. I would also check the gaskets on the ends of the intake manifold as I have seen some serious leaks back there.

If the car sat for a period I would seriously consider changing the PCV valve to be sure the engine is breathing okay. A plugged PCV valve can over pressurize the inside of your engine and force the oil and seal out of the engine.

If you are having a hard time finding the leak try using some GUNK and cleaning the bottom of the engine and watching it after it is dry again.
DO NOT wash the top of your engine or you risk getting water into a place that is not designed for it. I had to replace a very expensive alternator on a newer car when I cleaned the engine.... Instead it cleaned out my wallet....

Best Regards,
Chris

65Z01

Before you get it onto a lift you can visually check:
-oil pressure sender up top near distributor (LH side)
-rear of intake behind the China-wall
-under valve cover edges
-rear of oil pan, drain plug

Use a very strong light and lay down a large sheet of cardboard, top off oil and start engine and, based on the heavy leakage rate, I think you will easily locate the leak area.

Good luck, let us know how it goes.

ctmccloskey

After sitting for 8 years that is entirely possible for your rear main to start leaking. It is however unlikely as the seal is a tough little bugger and more prone to fail on higher mileage Corvettes. I am still betting on your leak being one of the more common ones like mentioned before.

Start the car and pull the oil filler plug out and see how much pressure is coming out of the oil fill hole. If there is a lot of leakage it would not be so surprising on an engine that sat for that long. The Blow by (if there is any at all) might slow down as the parts seat again inside the engine.

The PVC valve can be checked by simply shaking it, it should rattle as there is a spring inside of it. If it doesn't be sure to get a replacement as it is important to let the engine breath properly. (On my Mom's Volvo V70 with the High pressure Turbo it came with had a PCV fail and it cost her a new engine. The engine pressurized and blew it's cam seal out causing a loss of oil and an engine Lock-up.)

Before you put the car on a lift try and remove the excess oil on the bottom of your engine. A can of Gunk will do wonders in making it possible to see a oil leak, with the engine cool spray below the spark plug line only and on both side and the rear of the engine. I have wiped down engines so I could see the source of the leak. I have never tried or needed to use any dyes in the engine oil but that is another option.

After reading your original post again it is likely to be the oil cooler or the oil pressure sending units.
Do you have the set of Factory Service Manuals for your year Corvette? You might need them when it comes time to repair the leak.
I hope it something simple to see and even easier to fix!

Best of luck in finding the leak!
Chris

m257876

I *do* have the GM service manual for this car - the previous owner included it and the original owner's manual when I bought it.

What is "normal", in terms of flow rate, when you pull the oil drain plug with the engine running? I guess I could pull the plug and see how much comes out with the car not running, and then have somebody start the car while I'm watching to see if the flow rate increases a lot. Would that work?

I'll see about getting some GUNK this weekend and clean up the bottom of the block and start looking for the leak. I"ll also check the PCV valve. I'll post again out here when I've made some progress.

This car's nickname is going to have to have "queen" in it somewhere, with all the time it's going to sit in the garage over the near term.

Thanks,

Mark

Pwnage1337

Must be a troll? "Pull oil drain plug while running"

That's how I do all of my oil changes. Engine running, pull drain plug. That way you get all the oil out! Works best for engine longevity!

Pwnage1337

Make sure you touch your tongue to the exhaust pipes to see which bank might be running lean. Whichever pipe is hotter is running leaner than the other bank. Don't want to risk popping a piston! Could be sticky injector not firing quite right.

Hot Rod Roy

Pwnage, that's a simple mis-understanding! Go easy, the guy's learning!! And you call yourself a "Tech Contributor"?

Pwnage1337

Trolls be tricky these days... Lol

Sarcasm is a dangerous thing.

Why would anything be coming out of the oil fill hole with the engine off?

m257876

Hey - my mistake. I thought he meant the drain plug. The filler hole is clearly a safer way to do it. I'm not used to seeing "filler plug" terminology, and the "plug" part threw me off.

I guess my question now is - how do you remove the filler cap and then check if there's too much pressure? I don't have a fitting to fit the filler hole and hook up a pressure gage.

And I can take a joke - but honestly, after driving all the way home with oil streaming out the engine until it was nearly dry, pulling the drain plug for 5 or 10 seconds with a full crankcase seems pretty safe by comparison.

CorvetteRules

Shortly after buying my 91 at the end of last year I started to see oil smoke after a drive and looking from the top it appeared to be dripping on the drivers side heat shield on exhaust. Looked like a slow leak, but had it towed to the garage I use. I'm glad I did that because when they went to pull it into the garage bay it went from a slow drip to a gusher. It was the oil sensor on rear of block. Repair was cheap and simple. Unscrew sensor, screw new one in place.

arbee

Reading and comprehending what is written is a skill lost on a lot of people. At what point in this thread was it suggested to pull the fill plug with the engine off as claimed?

Pwnage1337

At what point in this thread did your mind turn to the idea that he was actually going to pull the "fill plug" and not the drain plug?

OP, sorry I jumped your ****, usually usernames with minimal letters and just a bunch of numbers are trolls. Given that you don't have a lot of post history, I made the assumption (wrongfully) that you were a troll and told you to lick your exhaust. Don't actually do that, you will **** up your tongue.

Jeremy

m257876

No harm done. I got busy the past couple days and was unable to do the lick test on the exhaust. (<-- that is sarcasm right there).

I'm still wondering how to assess things by removing the oil filler cap. Do I just hold the palm of my hand over the filler hole and see if there's pressure? Not sure I can judge how much is "too much." I guess I could compare it to my other vehicles or something. I've got a 2001 Toyota V6 that still runs great - maybe I'll compare the two.

I'll post again when I get some time this weekend and can get some work done on it.

Thanks everybody,

Mark

m257876

A few updates before real work starts:

I pulled the PCV valve out this morning and it is rattling just fine and the hose connections seem fine.

I shone a worklight back behind and under the back of the intake manifold, and from the driver side (near the wiper motor) I can see the oil pressure sender where it screws into the "stalk" or whatever that part is called. I can't see the oil pressure switch (wiring in the way), but the sender has oil on it, and so does the stalk. It is generally kind of oily all around and below that area. I can't quite see where the "stalk" connects to the back of the engine - the back part of the intake manifold is in the way looking at it from the driver side, and I can't see anything from the passenger side (under the dist cap). So whatever the "stalk" connects to is unobservable, and where all of it connects to the block is hidden also.

So, it's hard to tell how many of those threaded connections might be leaking, and In fact I can't even see if there are multiple parts and connections forward of the stalk. I think I am going to fill it up with oil and start it (maybe tomorrow or Sunday), and just take a look at that area to see if the pressure sender is leaking at its connection point, and whatever else exciting things might be going on in that area. Again, I can't see a lot with the manifold and the wiper motor in place. I guess I might grab a small mirror from Home Depot and see if that helps to see more toward the "forward" direction - where it all connects to the engine. I might be able to use that to push some wires around and see the oil switch connection, as well, on the other side of the stalk.

If it *is* leaking back there, I'll post again. It seems like that's going to be tough to get access to with the manifold and the wiper motor and the distributor all sitting right in the way. I guess I should be trying to find where the rear manifold gasket joints are, too, in case I can see those with the mirror.

More when I know it,

Mark

VikingTrad3r

Howdy OP and welcome. Welcome to c4 madness. So much fun to drive and cant beat the acquisition cost. but they do take work.

Fwiw, i have found that, inevitably, one thing leads to another, meaning you have an oil leak out the filter mount, rear china wall or the ops and more than likely you will need to remove the dizzy or the washer motor, my preference is the dizzy if you understand the importance of restabbing the exact same as it went in and if not how to restab a dizzy. (ccw twist as it comes out ...cw on way in...do i have that right?). and in the process of doing all of this you will either discover or create more work in the form of broken vac lines or plastics. especially if it is the rear of the china wall.

anyway im rambling a bit but the point is, be sure you have another car and are doing the job in a location that can handle waiting as you troubleshoot the unexpected likely by posting here. stripping bolts from overtightening is common, use torque specs and be ever aware of prior owners who have overtightened leaving a bomb for the next guy who pulls it out. its rare thag a job goes smooth a->b on an early c4. breaking vac lines most common. rubber vac line as a splice works best.

be prepared mentally is all im saying haha. many a c4 owner has lost steam when getting stumped.

if it were my car, id be pulling labeling the dizzy wires, using tape to mark exact losition of rotor and cap, and base, video the removal process, and id pull the wiper motor, and get eyes on the leak.

if you can wait, my guess is one of these would serve you well. i picked one up off amazon and they are great! i recently used it to ensure i had installed the clutch corectly snaking it into the bellhousing fork window. you could likely see active leaking while running the car. they do have a light you can activate.

Hot Rod Roy